Plugging of vugged and porous strata



April 23, 1958 M. E. CHISM 3,379,253

PLUGGING OF VUGGED AND POROUS STRATA Filed Aug; 16, 1965 2 Sheets-Sheet 1 .7 I INVENTOR MELVIN E. CHISM y A 7' TORNEYS April 1968 M. E. CHISM 3,379,253

PLUGGING OF VUGGEDAND POROUS STRATA Filed Aug. 16, 1965 2 Sheets-Sheet 2 F IG. 2 I INVENTOR MELVIN HIM BY E c s United States Patent 0 3,379,253 PLUGGING 0F VUGGED AND PORQUS STRAT A Melvin E. hism, Bartlesviile, Okla, assignor to Phillips Petroleum @ompany, a corporation of Delaware Filed Aug. 16, 1965, Ser. No. 479,837 8 Claims. (Cl. 166-33) ABSTRACT OF THE DISCLQSURE Vuggs encountered in formations when drilling a well are sealed off to prevent lost circulation by depositing in the well bore in the vugged area a solid foam-forming agent, foaming and solidifying the agent, and drilling thru the plugged well bore.

This invention relates to a process for plugging of vugged and porous strata around a wellbore during rotary drilling of a well.

In the petroleum industry rotary drilling of oil and gas wells using a mud or clay laden fluid circulated into the borehole to remove the cuttings and to assist in the drilling by lubricating and cooling the bit, is practiced. It frequently is necessary to drill thru large-pored, fractured, and vugged formations. When strata of this type are encountered in drilling, intolerable losses of drilling fluid will occur unless measures are taken to seal off the troublesome strata. Formations have been encountered in well drilling operations that were so highly vugged that it was impossible to even set cement to plug them off. All kinds of extreme measures have been tried on such formations including injecting burlap sacks, bricks, wire, rocks, etc. into the wellbore and forcing same downhole to plug off the vugged area.

This invention is concerned with a method or process for plugging and sealing off porous and vugged or fractured strata which result in excessive lost circulation of drilling fluid.

Accordingly, the principal object of the invention is to provide a process for plugging and sealing a vugged, fractured, or highly permeable stratum to prevent lost circulation while drilling a well. A further object is to provide a method of sealing a stratum around a wellbore which is not readily scalable by conventional methods. Other objects of the invention will become apparent to one skilled in the art upon consideration of the accompanying disclosure.

A broad aspect of the invention comprises depositing in a wellbore within a highly vugged, fractured, or porous stratum and in the surrounding vugs or other voids, a solid-forming and foaming agent such as polystyrene, foamed latex, and polyurethane, solidifying the agent in place, and thereafter drilling thru the plugged wellbore and continuing the drilling process. Polystyrene, foamed latex, and polyurethane are well known, commercially available materials and the processes for forming these materials are likewise known in the art and will not be discussed in detail. I

A convenient procedure for positioning the foamed solid in the vugged area comprises packing off the Wellbore around the drill pipe just above the level of the vugged stratum and injecting the foam producing materials thru the drill pipe into the wellbore below the packer so as to force the material into the vugs. Several methods can be used to introduce the required chemicals into the wellbore and vugged area surrounding same. These include (l) premixing the foam producing materials at the surface, including a retarding agent, and pumping the required or calculated volume down the drill string to the hole below the packer; (2) pumping the different required 3,379,253 Patented Apr. 23, 1968 chemicals down separate small pipes or hoses run inside the drill pipe (these pipes extending to just below the packer and being provided with nozzles for intermixing of the chemicals); and (3) dropping chemicals to the zone below the packer in commercially available, self-rupturing, plastic canisters, the different reactive materials being alternately dropped to provide suitable mixing and distribution of the reacting chemicals.

A more complete understanding of the invention may be had by reference to the accompanying schematic drawing of which FIGURE 1 is an elevation in partial section thru a well in which foamed solid has been positioned in accordance with the invention and FIGURE 2 is a similar view illustrating another embodiment of the invention.

Referring to FIGURE 1, a vugged stratum 10 is penetrated by a well 12. A drill string or a pipe 14 extends from ground level to a position adjacent the upper level of stratum 1t) and is provided with a packer 16 packing off annulus 18 above stratum lfl. Vugs 2i) and the wellbore below packer 16 are filled with foamed solid 22. The foamed solid is formed in place by any of the procedures outlined above. After filling the vugs 20 with foamed solid, packer 16 is removed from the well and rotary drilling is continued, the foam in the wellbore being readily drillable. During subsequent drilling, there is no lost circulation to the vugs in stratum 10.

In FIGURE 2, corresponding numbers are used to designate corresponding elements of FIGURE 1. A liner 24 is hung from an upper string of easing (not shown) so that it extends substantially thru stratum 10 which is to be sealed off. A packer 26 is positioned on the lower end of the drill string 14 to seal off the annulus 28 formed between the drill string and liner 24. A foam 22 is formed in situ in vugs 2i and in the annulus 30 surrounding liner 24. This is done as heretofore described by injecting the solid foam forming materials thru drill string 14 and following the injected slug of foam forming material with a slug of cement conventionally utilized in cementing casing in a Well. The cement drives the foam forming material up annulus 30 and into vugs 20. Because of the sealing off of the upper end of annulus 30 Where the liner is attached to the casing string, the foam forming material is forced into vugs 20 because of the build up of gas pressure in annulus 30 above stratum 10. The injected cement 32 takes the position shown in the drawing, extending up annulus 30 behind liner l4 and filling the lower end of well 12. After the cement has set, packer 26 is withdrawn and drilling is continued thru cement plug 32, leaving the vugged formation 19 sealed off to prevent loss of drilling fluid.

Generally, the liner of FIGURE 2 is necessary when a vugged stratum is encountered in drilling to great depths where the drilling fluid pressure is great. Usually highly porous, vugged, or fractured strata are encountered near the surface Where the solid foams provide adequate sealing and protection against lost circulation under the pres sures involved. Hence, the invention has greater application at shallow depths.

Further information regarding the formation of foamed solids may be found in the literature, particularly, in Kirk-Othmer, Encyclopedia of Chemical Technology, Interscience, volume 13 for polystyrene foams (1954) ibid., volume 11 for latex foams (1953); and ibid., volume 14 for polyurethane foams (1955).

One technique comprises injecting into the Well bore adjacent the vugged section a latex containing foaming and gelling agents. Another technique comprises whipping a latex to a light foam and injecting same along with a gelling agent to effect solid foam formation. In a further technique, a polyester of a dicarboxylic acid and a trihydroxy alcohol and a diisocyanate are injected thru separate conduits and mixed downhole to form polyurethane within the vuggs.

Certain modifications of the invention will become apparent to those skilled in the art and the illustrative details disclosed are not to be construed as imposing unnecessa y limitations on the invention.

I claim:

1. A process for plugging a vugged stratum around a wellbore which comprises the steps of:

(1) depositing in said wellbore within said formation and in the surrounding vuggs a solid foam-forming agen-t comprising essentially a latex containing foaming and gelling agents;

(2) solidifying the agent of step (1) in place; and

(3) drilling thru the plugged wellbore resulting from step (2).

2. The process of claim 1 wherein the agent of step (1) is polystyrene.

3. A process for plugging a vugged stratum around a wellbore which results in lost circulation in continued rilling of said wellbore with rotary drilling equipment using a hollow drill string and drilling fluid, comprising the steps of:

(1) setting a packer on said drill string just above the level of said stratum to seal off the annulus around said string;

(2) injecting solid foam-producing materials comprising essentially a latex containing foaming and gelling agents thru said string into the wellbore below said packer and into the vuggs in the surrounding stratum;

(3) converting the material in step (2) into solid foam;

and

(4) thereafter, drilling thru the foam in said Wellbore.

4. The process of claim 3 wherein the solid foamprodueing material comprises granular polystyrene and step (3) comprises heating the granular polystyrene in place.

5. The process of claim 3 wherein latex is whipped to a light foam and same is injected in step (2) along with a gelling agent to effect solid foam formation in step (3).

6. A process for plugging a vugged stratum surrounding a \vellbore which comprises the steps of:

(l) positioning a metal liner in said wellbore extending from substantially above said stratum to the bottom thereof;

(2) injecting a solid forming foam producing agent into said wellbore below said liner so as to force same into the vuggs behind said liner and a following slug of cement so as to position the interface between said cement and said agent behind the lower section of said liner;

(3) solidifying and foaming the agent of step (1) as positioned in step (2); and

(4) allowing said cement to set so as to seal off the vugged stratum.

7. The process of claim 6 in which poly-urethane foamproducing ingredients are simultaneously and separately injected thru separate conduits extending thru said drill string and mixed in place to produce poly-urethane foam.

8. The process of claim 7 in which a polyester of a dicarboxylic acid and a trihydroxy alcohol is injected thru one conduit and a diisocyanate is injected thru a second conduit and mixed downhole to form the polyurethane.

Refereuces Cited UNITED STATES PATENTS 2,274,297 2/1941 Irons et al. 166-33 X 2,502,191 3/1950 Williams 166-33 X 3,141,513 7/1964 Davis 166-33 X 3,181,611 5/1965 Dollarhide 166-33 3,181,612 5/1965 West et al. 166-33 3,299,953 1/1967 Bernard 166-29 3,306,356 2/1967 Sparlin 166-33 2,761,511 9/1956 Billue 166-33 X OTHER REFERENCES The Condensed Chemical Dictionary, sixth edition, Reinhold Publishing Corporation, New York, N.Y., 1961 (page 919 relied on).

STEPHEN J. NOVOSAD, Primary Examiner. 

